The invention relates to a mechanical press for fine blanking, forming and/or stamping of work pieces, the press having a machine frame assembled of a head piece and an O-shaped frame, a fine blanking or forming head with a fixed upper tool part suspended from the head piece and projecting into the O-piece, a ram vertically guided on a stroke axis in the O-shaped frame provided with a table top for fixing a lower tool part and a positioned below the ram toggle mechanism.
DE 199 35 656 A1 discloses a line of presses with a modified position above a table toggle mechanism which is driven via an electric motor by an eccentric shaft rotatably run on bearings provided with a torsion rigid eccentric and using an interconnected flywheel. The eccentric has a connecting rod with a respective connecting rod bearing. The connecting rod at its end not adjoining the eccentric has a head, on which are developed two bearing points arranged apart from each other. These bearing points, with the center of the connecting rod, define a triangle. A first splicing plate is connected via a bearing pin to the head piece of the machine frame, providing a fixed bearing. The other end of the splicing plate is pivoted to the connecting rod by another bearing pin. A second splicing plate is attached to the ram at one end and to the connecting rod at the other end. The fixed bearing of the modified toggle is positioned above the press ram and the articulation point allocated to this fixed point swivels around this fixed point. The upper articulation point defines a curved path. Such a modified toggle mechanism causes ram movement to slow down, so that the material in the lower dead point has enough time for plastic flow.
However, it is disadvantageous that the fixed bearing of the splicing plate allocated to the connecting rod and the ram lie on different axes and further that the fixed bearing for the eccentric shaft is positioned near the ram. As a result, in the upper dead point, an almost effective length of the splicing plates can not be achieved, so that the rigidity and thus the power transmission onto the ram is always accompanied by horizontally acting force components, whereby the ram wear and also the power applied to the ram have to be increased. This has negative consequences for the machine frame, which has to be designed to be more massive, and for the driving power of the motors, which have to achieve higher turning moments.
FIG. 1 shows toggle press 1 as disclosed in DE 199 35 656. In a machine frame 2, a vertically movable ram 3 is positioned. Below the ram 3 is positioned a table 4 (see FIG. 2) which is attached to the machine frame 2. The table 4 is used for taking up a lower tool and the ram 3 is prepared for taking up an upper tool.
The ram 3 is actuated by a ram drive which includes a modified toggle mechanism 5 driven by an eccentric shaft 6, in turn driven via a transmission means, for example a toothed wheel, and by an electrical motor. Between the electrical motor and the toothed wheel an attached transmission gear, an epicyclic gear, for example, can be positioned.
The kinematics of the toggle mechanism 5 can be seen from FIGS. 1 and 2. On the eccentric shaft 6, which is turnable on a bearing position L1, an eccentric element 7 is positioned. Attached to the eccentric element 7 is a connecting rod 8 provided with a connecting rod bearing 9. The connecting rod 8 at its end distal to the eccentric element 7 has a head 10, at which two bearing positions 11 and 12 are distanced from each other. The bearing positions together with the center of the connecting rod bearing 9 define a triangle, as shown in FIG. 2 where the respective distances are referred to as distances E5, E6 and E8. The eccentricity of the eccentric element 7 is indicated by reference point E4. The eccentric shaft 6 is turnable around a rotation axis D, which is fixed in the machine frame 2. Thus, L1 defines the fixed bearing for the eccentric shaft 6.
The connecting rod 8 is connected by link bars 13 and 14 to the machine frame 2 and to the ram 3. The link bar 13, through bearing pin 15 pivotally attaches arm 13 to the connection area 16 of the connecting rod 8, and bearing pin 17 attaches arm 13 to the machine frame 2. Bearing pin 17 of the link bar 13 forms a fixed bearing L2 which is positioned above the ram 3 and table 4. The link bar 13 in FIG. 2 is referred to as E7. Link bar 14 at its one end pivots around a bearing pin 18 in the connection area 19 of connection rod 8, and the other end of articulated arm 14 pivots around a bearing pin 20 in the ram 3.
The fixed bearing L2, that is the fixed point, with which the articulated arm 13 is fixed to the machine frame 2, does not lie on the vertical stroke axis HU of the ram 3. Thus, link bars 13 and 14 do not reach a sufficient effective length at the upper dead point OT, so that operation translates in part to an unwanted horizontal force component applied to the ram 3. This adversely affects the useful life of the ram and contributes to a reduction in force that the ram can apply in the fine blanking or forming operation. This leads to higher turning moments, in order to compensate for the generation of unwanted horizontal force components. Also, to compensate, the machine frames must be made more massive, that is, made with higher weight and stability, in order to compensate for the horizontal forces.